Tire tread



Dec. 14, 1954 E, s, EWART ErAL 2,696,863

TIRE TREAD Filed June 2o, 1951 2 sneets-sheet 1 INVENTOR. ELLIOTT S. EWART BY AUDREY H. STEADMAN ATTORNEY.

Dec. 14, 1.954

E. S. EWART ETAL TIRE TRED Filed June 20, 1951 2 snee'ts-sheet 2 l |5 I4 l IO lulo Vlllllllllll/A I3 vmnmlnm Lely INVENTOR. l lo ELLIOTT s. EwART |4722 n4 I5 23 BY AUDREY HSTEADMAN I/gjm M&4. mm

ATTORNEY.

United States I atfitf"50,r

TIRE TREAD Elliott S. Ewart, St. Clair Shores, and Audrey H. Steadman, Detroit, Mich., assignors to United States Rubber Company, New York, N. Y., a corporation of New Jersey Application June 20, 1951, Serial No. 232,633

2 Claims. (Cl. 152-209) This invention relates to tires, and more particularly it relates to the construction of the tread portions of t pneumatic vehicle tires.

Heretofore many attempts have been made to design and construct the treads of pneumatic tires to improve their skid resistant properties while preserving the tread wearing qualities and stability of the tire and without Another object of this invention is to provide a tire having a tread presenting a greater face area for road engagement resulting in longer tread wear and superior traction properties.

A further object of this invention is to provide a tire tread having functionally continuous, circumferentially extending, undercut ribs forming relatively deep constricted grooves therebetween which function to provide a iiexible cushion effect enhancing the riding qualities while maintaining the stability of the tire.

A further object of the invention is to provide a tire having a tread structure comprising circumferentially extending undercut ribs, provided with circumferentially extending slits in the central area of the rib tread surfaces forming laminations, flanked on both sides by cross-slots extending inwardly from the marginal edges of each rib, all of which combine functionally to provide quicker gripping action, greater road contact area, and higher resistance to both forward and lateral skids.

A further object of the invention is to provide a tire tread formed with undercut ribs and constricted grooves providing increased tread unit flexibility and a softer ride, said ribs being designed and adapted to buttress one another under severe lateral skid conditions assuring good tire stability. t

A still further object of the invention is to provide a tire having a tread structure including ask-shaped or constricted grooves having relatively wide bases and narrow face openings which minimize groove cracking and inhibit stone pickup.

A further object of the invention is to provide a tire having a tread structure including circumferential ribs undercut to provide overhanging edge portions and relatively closely spaced cross-slots in said edge portions forming units of small base length which during tire operation provoke a lower volume of noise and provide quieter tire performance.

The above and other objects, advantages, and novel features of this invention will be made more apparent as this description proceeds, especially when considered in connection with the accompanying drawings, wherein:

Fig. 1 is a plan view of a portion of a pneumatic tire illustrating an embodiment of this invention;

Fig. 2 is a transverse sectional view taken substantially on the plane indicated by line 2-2 inFig. l;

Fig. 3 is a fragmentary perspective view of a portion of the tire tread;

Fig. 4 is a fragmentary transverse sectional view through the tire tread as it appears under load conditions;

Fig. 5 is a view similar to Fig. 4 showing the tire tread Patented Dec, 14,., 1954 as it appears under load when engaging road irregularities;

Fig. 6 is a fragmentary transverse sectional perspective view of a portion of the tire tread as it appears under lateral skid conditions;

Fig. 7` is a fragmentary circumferential sectional View taken on line 7 7 in Fig. 2; and

Fig. 8 is a view similar to Fig. 7 showing the tire tread as it appears when the brake is applied.

Referring to the drawings and more particularly to Figs. 1 to 3, there is shown a pneumatic tire comprising the usual carcass 10 having inextensible bead elements 11, sidewalls 12 and a tread portion 13 formed of rubber or rubber-like material. Asy shown, the tread is divided into a plurality of functionally continuous circumferentially extending ribs 14 separated by relatively deep grooves 15. The outermost ribs 14a of the tread are buttressed by respective rubber structures extending to the sidewalls of the tire, and said structures may be formed with suitable grooves 16 and ribs 17 arranged to form an ornamental or distinctive design. t

As shown, the grooves 15 are relatively deep and of substantial width at their bases. Each groove is substantially flaskshaped in cross section having a relatively Wide base portion 18 and a narrow or constricted face opening 19 at the tread face area. To provide grooves of this character, the ribs 14 are undercut as shown to provide substantially continuous overhanging edge or side portions 20 forming abutments, the faces 21 of which are adapted to abut so that the ribs will buttress one another under severe lateral skid conditions as will be more fully explained hereinafter.

, Each of the ribs 14 as well as outermost ribs 14a are provided with a plurality of circumferentially extending, relatively shallow and closely spaced slits 22 forming thin or narrow laminations 23. The slits 22are made without removing any rubber from the tire and withoutmaterially changing the appearance of the tread surface in the slitted area. The number of slits 22 in each rib may be varied, preference being given, however, to the arrangement illustrated in which the two ribs 14 adjacentthe out ermost ribs 14a are provided with four slits, whereas the remainder of the ribs are provided with three slits each.

The width and height of the laminations 23 are important because their purpose is to increase the softness and flexibility of the tire surface in the vicinity of such surface so as to provide a flexible cushion effect enhancing the riding qualities of the tire and to cooperate, in a manner yet to be described, in resisting lateral skids. The slits 22 are cut to about 1/3 the anti-skid depth of the tread andare spaced approximately JAG" apart.

In `order`to further improve the traction properties and increase the skid resistance of the tread, each rib 14 is provided with a plurality of relatively closely spaced cross slots 24 extending inwardly from the marginal edges thereof toward the central rib area occupied by theV laminations 23. The inner edges of the outermost ribs 14a are also provided with similar cross slots. These cross slots 24 are located in the overhanging edge portions 20 of the ribs 14 and 14a and the slots 24 in adjacent rib surfaces are opposed to one another. These cross slots 24 are spaced to form or define segments or units 25 of small base length. The base length of the units 25 is important and if, as illustrated, a base pitch of substantially .4 inch is employed, the shortest unit would be substantially .3 inch and the largest substantially .5 inch. This relatively close spacing of the cross slots 24 reduces the circumferential compression wave of each unit 25 and when the compression strains are released at the slot edges 24, during rotation of the tire in use, the resulting snapping action produces a lower noise volume than when longer base units 25 are employed. This results in quieter tire performance.

As shown in Figs. 2 and 3, the cross slots 24 in the opposed faces of adjacent ribs are arranged opposite one another in pairs and their radially inner ends merge into the large base portions 18 of the grooves 15. These slots are usually arranged in groups irregularly spaced around the circumference of the tire to break up the pitch noise. The depth of the cross slots transversely of the tire tread is substantially equal to the thickness of the overhanging edge portions of the ribs 14 and 14a. Thus, the units 25, previously referred to, may act individually and in cooperation with adjacent units'to prevent or reduce forward skid of the tire. Also, the faces 21 of the units 25 of adjacent-ribsA are adaptedfto-buttress oneanother-under severe lateralrskid conditions to insure tire stability oda highA order.

Under normal 'road' and f load conditions, disregarding skid forces, the tread will perform-in-the areavof'road engagement substantially-asillustrated-in-Figw4. If unusual loads or lateral forces areencounteredY the faces 21V-ofthe overhanging portions-2W of the units 25wvill abut with the resultthattheantiskid^elementsfof=the tread are-supportedvforlbuttressed by-one anothento--insureegoodv tire Stability.- This construction permits-the use of-anti-skid elements ofgreaterv height withha correspondingly substantial increase in 4tread-,Wear `without impairingthey stability of the tire.'

IfJ the-road surface-is Arough-L on uneven and other conditionsarelthesame, thetreadsurfacewilllperformina f mannerssubstantiallyhas illustrated -in-Fig. 5A.v Thev flexibilityimparted to l.the tread by reason offthe slits -22 and laminations 2 3' permitslthetreadfto=A adaptitselftouneven roadv conditions-andato produce-a*gripping'action resulting in higher traction properties.-v

In-Fig. 6 theaction offthetread-'is -illustr-atedfa's it functionslundert4 lateral'skid conditions.-Ik In this illustration it is `assumed zthat the- Skidis in the directonLofithe-arrowt The undercut-tread ribs 414 being-relativelyy laterally flexible-tend'ttoleanover or-bendy laterally inadirection opposite to thedirectionof the skid, the greatest'ribmovement ybeingl at be-tread surface where theA ribs areseparated bythe relatively-narrowslots-19v Hence,-und er severe lateralskid-conditions,` the-fa`ces 211of -the units V of one rib-will engage-the-opposediaces 2 1ofthe next adjacent rib and be buttressed thereby. At the Same time, the laminations-23 Vare laterallydisplacedto move the-exposedend faces ofthe laminations outvofiplanar alignment thereby producing -a corrugated orroughened surfaceon the exposed faces of 'the .ribs14.- This -materially enhances theskid 'resistance/'properties `of fthetire;

By la comparison of Figs.- 7--andf8 the action of--the tread, when-the wheel brake-is applied, can-be observed. As -shown -inFigf 7, the .units-25 are, underA normal conditions,` circumferentially separated by-thef-crossfslots- 24: However if the wheel is traveling in the direction of the arrowinFig. 8, and the'brake-is applied,vthe.-units.25 will be distorted out of theirnorrnalspaced relation `into-*substantially the. angular positions illustrated in Fig, 8 wherein the leading edge portions ofeachunit-ZS :willbe presented for. positive anti-skidengagement withthe road surface. While the wheel iS-.beingpowerdriven; thetrail-l ing edge portions of eachunit: 25 will-functionzima like manner.

Tires having treads constructed -in accordance-with this invention have softer riding qualities,- low noiservolume, superior skidy resistance` and hightraction properties. Theundercut ribs provide tread groovesfhavingvwide bases and-,narrow faceopenings whichfminimize groove crackingand inhibit stonet-pickfup. This` construction 4'; also provides a greater road contact area resulting in longer tread Wear.

The flexible undercut ribs combine functionally with the cross slots to render these slots more effective in minimizing forward Skid motion and with the circumferential slits to make thesey slits more free-acting in inhibiting lateral skids. Also, with this tread design the over-all stability of theltire is .maintained because of the buttressing action of the ribs. This permits the use of anti-'skid-1elernents of-greater height with` the corresponding-Yincreasefin-tread wear; The cross-slots will continue to-b'e effective until-the `tread Iis.. substantially vworn away and if the circumferential slits are renewed thev tread will remain highly exible and skid resistant to the end of its anti-skidlife` Having thus described ourl invention, what we claim and desire to protect by Letters Patent is:

1. A tire having a tread comprising a plurality of circumferentially extending-A` ribs dening grooves therebetween, sometoffsaid ribs beingundercut onbothsides throughout their length to provide overhanging-rnarginal portions at: the road-engaging;` surface..A of theribsd which extend-into the tgrooves-in contiguous .relation tothe-marginal portions .of adjacent ribs, saidfribs -being relatively laterally fiexibleand saidtmarginahportions -adaptedto contact. each .other t under unusual floads -or severe lateral stress, the.road-engagingsurface of saidA ribs between .said over-hanging portions being-,slit circumferentially Ato form an plurality of relatively thin; laminations to impart Surface flexibility and additional lateral exibility to saidribs, and'relativelynarrow,v circumferentially arranged, closely spacedaslots. extendingtransversely,v through said over hanging. portions` to a point adjacent Said slittedgarea to divide `the same t .into units functioning separately under tangential stress 2; At tire, .tread .comprising` aplurality of ycircumferentiallyJextendingribs defininggrooves therebetween, some of said ribs being undercut on bothzsideS-throughout thenlength-totimpart `lateralexibilityathereto and to formfsubstantiallycontinuous overhanging edge portions formingagtjoovesbetween.adjacent ribs having relatively wide Aba'sestand narrow. face openings, said edge portions ofadjacent ribs 4 abutting :when under-lateral stress to buttress one another, the.,-road:engaging surfaces `of-saidribs being slit.; circumferentially` in: the area :between `Saidoverhanginggportions to form a; pluralityvof relatively A thin laminationsflto-a-impart surface flexibility to .said :ribs, and relativelyv narrow',l circurnferentially,4 arranged,v closely spacedcrosls,Sl0.tS.in:-said overhanging portions defining unitstof relativelyj Smallbase. lengthfunctioning-separately-under` tangential ',stressl References ,Cited inthe, file of thisl patent` UNITED STATES ,BATENTS.

Numbers Name Date D` 112,346l MooradianvA Nov. 29, 1938 2,094,636; Bull Oct. 5, 1937 2,272,879 Hargraves Feb.: l0, 1942 2,l` 22,1,5, 05,v vBull .June 22, 1943 

